BEIRUT, Jan 10 (Reuters) - The United Nations World Food Programme has pressed the Syrian government to increase access to besieged residents in Damascus and Aleppo, its chief said, while in eastern Syria a surge of fighting has made regions there more difficult to reach.

WFP head Ertharin Cousin said late on Thursday that the U.N. food agency aims to raise its target population in Syria to around 4.9 million in 2014, as the conflict between President Bashar al-Assad and the rebels seeking to oust him goes into its third year.

In November, the agency said it had reached 3.3 million people.

After returning from a trip to Damascus, Cousin told Reuters that state officials responded positively to requests for access. Her aim was to increase planning and cooperation to ensure those promises were implemented, she said.

"What I talked about with the government were very tactical ideas of how do we get into Aleppo using different roads ... we talked about how do we reach those areas of rural Damascus where the regime government has said we can go. How do we then work with those checkpoints to get into those areas?," she said in an interview in Lebanon.

Over the past year, some rebel-held suburbs outside Damascus were under siege by Assad's forces, leaving residents struggling to find food.

Critics and some aid workers have said that government forces aimed to starve the area of food supplies and force out their opponents in a way that indiscriminately hurt civilians. Local doctors reported several cases of children dying from malnutrition.

Cousin said she was hopeful that the government would allow more access to the WFP in the coming year.

"I'm going to believe their commitments, that they're going to allow us to move into more of those areas in the future, because the need is not reducing, the need is increasing."

UNTENABLE AIRLIFT COSTS

Even as the prospects for access appeared to be improving in northern Aleppo and central Damascus, Cousin said large swathes of eastern Syria had become even harder to access due to hardline Islamist rebels taking some of the main roads in the area.

U.N. agencies launched a series of airlifts into the northeastern province of Hassaka in December, but such moves would be too costly to sustain, especially if they were extended to the other eastern provinces of Raqqa and Deir al-Zor.

Last month, the WFP said it flew 12 shipments of food from the Iraqi Kurdish city of Arbil into Hassaka province. Cousin said it still not enough to meet requirements in Hassaka alone.

"Twelve flights gave us enough food for 6,000 families. There are 45,000 families in Hassaka that need assistance," she said.

"We have estimated that in order to use that same methodology on a monthly basis to reach those families, that's $6 million a month to airlift food to 45,000 people. And that doesn't even cover the people in Deir al-Zor or Raqqa."

More than 100,000 people have died in the unrest in Syria, which began as an uprising against Assad family rule in March 2011 and became an armed conflict after Assad's forces cracked down on demonstrations. About 2.4 million have fled Syria and fighting has displaced more than 4 million others inside the country.

International powers are hoping to bring Syria's warring sides together for a peace conference later this month, but the prospects of a negotiated solution still seem dim.

The WFP chief said her agency was now developing projects required during long-term crises. It plans to target pregnant and breastfeeding women to provide nutritional help to young children in their most critical first years.

"If they don't receive the nutrition required in their first thousand days, that's irreparable damage to the child," she said. "The child will be mentally and physically stunted for the rest of its life." (Editing by Susan Fenton)